#先定一个node的类
class Node():                  #value + next
    def __init__ (self, value = None, next = None):
        self._value = value
        self._next = next
 
    def getValue(self):
        return self._value
 
    def getNext(self):
        return self._next
 
    def setValue(self,new_value):
        self._value = new_value
 
    def setNext(self,new_next):
        self._next = new_next
 
#实现Linked List及其各类操作方法
class LinkedList():
    def __init__(self):      #初始化链表为空表
        self._head = Node() 
        self._tail = None
        self._length = 0
 
    #检测是否为空
    def isEmpty(self):
        return self._head == None  
 
    #add在链表前端添加元素:O(1)
    def add(self,value):
        newnode = Node(value,None)    #create一个node（为了插进一个链表）
        newnode.setNext(self._head)   
        self._head = newnode
 
    #append在链表尾部添加元素:O(n)
    def append(self,value):
        newnode = Node(value)
        if self.isEmpty():
            self._head = newnode   #若为空表，将添加的元素设为第一个元素
        else:
            current = self._head
            while current.getNext() != None:
                current = current.getNext()   #遍历链表
            current.setNext(newnode)   #此时current为链表最后的元素
 
    #search检索元素是否在链表中    
    def search(self,value):
        current=self._head
        foundvalue = False
        while current != None and not foundvalue:
            if current.getValue() == value:
                foundvalue = True
            else:
                current=current.getNext()
        return foundvalue
 
    #index索引元素在链表中的位置
    def index(self,value):
        current = self._head
        count = 0
        found = None
        while current != None and not found:
            count += 1
            if current.getValue()==value:
                found = True
            else:
                current=current.getNext()
        if found:
            return count
        else:
            raise ValueError ('%s is not in linkedlist'%value)
 
    #remove删除链表中的某项元素
    def remove(self,value):
        current = self._head
        pre = None
        while current!=None:
            if current.getValue() == value:
                if not pre:
                    self._head = current.getNext()
                else:
                    pre.setNext(current.getNext())
                break
            else:
                pre = current
                current = current.getNext()
 
    #insert链表中插入元素
    def insert(self,pos,value):
        if pos <= 1:
            self.add(value)
        elif pos > self.size():
            self.append(value)
        else:
            temp = Node(value)
            count = 1
            pre = None
            current = self._head
            while count < pos:
                count += 1
                pre = current
                current = current.getNext()
            pre.setNext(temp)
            temp.setNext(current)
    

    # printf 打印链表
    def printf(self):
        answer = []

        current = self._head
        while current:
            answer.append(current.getValue())
            current = current.getNext()
        
        for ans in answer:
            print(ans)


def main():
    L = LinkedList()
    L.append(0)
    L.append(1)
    L.append(2)
    L.append(3)
    L.printf()
    print("====================")
    L.remove(2)
    L.printf()




if __name__ == '__main__':
    main()